The right ventricle receives blood from the right atrium through the tricuspid valve and pumps the blood through the pulmonic valve to the pulmonary artery. In pumping blood, the right ventricle expands during diastole to take in blood through the tricuspid valve and contracts during systole to discharge blood through the pulmonic valve into the pulmonary artery.
It is sometimes necessary or desirable to determine the effectiveness of the right ventricle in pumping blood to the pulmonary artery, and for this purpose, right heart ejection fraction is determined. Ejection fraction is determined by comparing the expanded volume or end diastolic volume (EDV) of the right ventricle with the contracted volume or end systolic volume (ESV) of the right ventricle. Mathematically, ejection fraction (EF) can be expressed as follows: ##EQU1##
Ejection fraction is calculated from thermodilution curves by hand computation. Thermodilution is typically carried out by injecting a cold indicator into the right ventricle or right atrium and allowing the indicator to be diluted with blood. As this cold mixture is pumped through the right ventricle into the pulmonary artery, the temperature of the fluid in the pulmonary artery falls and then rises. The temperatures of the fluid in the pulmonary artery are measured during the time that the temperature is rising and compared with a prebolus baseline temperature of blood in the pulmonary artery to establish temperature differentials. The temperature differentials are then used to determine ejection fraction. Ejection fraction calculation is widely discussed in the literature, such as
1. Journal of Surgical Research, "Measurement of Ejection Fraction by Thermal Dilution Techniques", H. R. Kay et al, Vol. 34, 337-346 (1983). PA1 2. The Journal of Trauma, "Thermodilution Right Ventricular Volume: A Novel and Better Predictor of Volume Replacement in Acute Thermal Injury", J. A. J. Martyn et al, Vol. 21, No. 8, 619-626 (1981). PA1 3. ASA, "Ejection Fraction By Thermodilution" (Abstract), G. G. Maruschak et al, Vol. 55, No. 3, September 1981.
Hand calculation of ejection fraction is typically performed using the plateau method which can be mathematically stated as follows: ##EQU2## where, T.sub.i is the temperature at any of the plateaus on the downslope (i.e. during the time the temperature in the pulmonary artery is rising) of the thermodilution curve, T.sub.i+1 is the temperature at the immediately following plateau, and T.sub.B is the baseline temperature. Hand calculation of ejection fraction using the plateau method is, of course, slow and, as shown by equation 2, utilizes only two points in the cardiac cycle, see American Journal of Cardiology, "Usefulness and Limitations of Thermal Washout Techniques in Ventricular Volume Measurement", E. Rapaport, Vol. 18, 226-234, August 1966.
In addition, calculation of ejection fraction using the plateau method is consistently lower than ejection fraction as calculated using radionuclear techniques. Accordingly, it is desirable to refine the ejection fraction determinations so that more accurate results are obtained.